1. Field of the Invention
The present invention relates to a lens apparatus, and more particularly, to a zoom-cam mechanism for a zoom lens apparatus.
2. Description of the Related Art
An example of a unit widely used to move a zoom lens unit in a zoom lens includes a cylindrical cam mechanism. A cam groove having a locus of an optical axis of the zoom lens unit is provided in a circumference of a cylindrical cam. When the cam rotates, the zoom lens unit moves on the optical axis along the locus of the cam groove to perform a zooming operation. A stopper mechanism in which a stopper part provided on the cam is in contact with a stopper provided in a housing rotably holding the cam is used as a unit for limiting a wide angle end and a telephoto end during the rotation of the cam. In this case, a limited rotation angle of the cam is approximately 330°.
When a zoom ratio of the zoom lens increases to lengthen a stroke length of the zoom lens unit, an arranged angle of the cam groove becomes a larger angle relative to the rotation direction of the cam, and hence a rotating torque of the cam increases. When the stroke length of the zoom lens unit is to be lengthened without the increase in rotating torque of the cam, a diameter of the cam or a rotation angle range of the cam may be increased. However, the increase in diameter of the cam causes increases in outer dimension of a product and mass of the cam. Therefore, the rotation angle range of the cam should be desirably increased. In the case of the conventional stopper mechanism, a maximum rotation angle limit of the cam is approximately 330° at most as described above.
An example of a stopper mechanism having a large rotation angle range is disclosed in Japanese Patent Application Laid-Open No. H09-070778.
In the conventional technology disclosed in Japanese Patent Application Laid-Open No. H09-070778, when the cam mechanism is provided with a rotation angle range which exceeds 360°, an external diameter of the cam increases because of a rotatable intermediate ring which is further provided outside a rotation member. For example, when a mechanism serving as the intermediate ring is provided to the cam in the both sides of the cam in the rotation axis direction, a total length in a cam shaft direction lengthens. Therefore, in a case of a zoom lens in which front and rear lens units are close to each other with little margin, the mechanism is likely to interfere with the lens units and thus is not suitable for practical use.